Inverters are—inter alia in PV-systems—used to convert the DC current into AC current conformal for feeding into an energy supply grid. In particular, inverters of high-power, like those used in solar farms, comprise a housing formed as a cabinet. Typically, ambient air is used as cooling air for heat generating electric and/or electronic components of the inverter. For this purpose, the inverter comprises a cooling air channel extending through the housing of the inverter. The beginning and the end of the cooling air channel are associated with an air inlet and an air outlet, respectively, disposed in a wall of the housing, for example the back wall or a sidewall. Within the housing, the cooling air channel runs along the components to be cooled, folded where required, in order to remove heat generated during operation by the cooling air. By a folded implementation, for example a meander-like implementation of the cooling air channel, its length within the housing may be increased and it may be achieved that the cooling air channel runs along all components to be cooled. The contact between the cooling air flowing through the cooling air channel and the components to be cooled may be optimized and the speed of the airflow of the cooling air may be increased. Both effects result, on average, in an improved cooling effect at a given volume flow of the cooling air.
The housing of the inverter may be separated into multiple chambers by partition walls, such that the chambers may be assigned to different protection classes with regard to their sealing against the ambient. For example it is known to separate the housing of the inverter into two chambers, wherein the mentioned cooling air channel extends through one of the chambers, while the further chamber is hermetically sealed against the ambient. The sealed chamber receives the sensitive components of the inverter, which usually are the electronic components. A circulating cooling airflow may be established within the sealed chamber, wherein a heat exchanger is provided for cooling the circulating cooling airflow in the sealed chamber by the ambient cooling airflow guided through the cooling air channel.
In an inverter, a cooling requirement exists in particular for the power semiconductor of the inverter bridges. Since high-power inverters like the above-mentioned inverters of solar farms are polyphase inverters, a plurality of inverter bridges are used that may be collectively also referred to as a stack. Further components having an increased cooling requirement within the inverter are inductors, also referred to as inductor coils, of output current filters and/or of DC converters of the inverter. Output current filters are used to smoothen the output current signal and therefore are also referred to as sinus filters. DC converters may be arranged upstream of the inverter bridges in order to increase the input voltage present at the inverter (boost converter) or to decrease the input voltage (buck converter). They use inductor coils as an energy store during conversion of the voltage.
Within the cooling airflow, inductor coils are usually arranged downstream of the stack, since the stack has an increased cooling demand and requires cooling air at a lower temperature level. Frequently, the problem arises that the amount of cooling air is not optimal for both, the stack and the inductor coils.
In document DE 41 06 684 A1, an air cooling concept for the field of automotive is described for feeding air to several units. The possibility is given to guide different cooling airflows sectionwise in parallel in order to adjust the air demand of components to be cooled individually by valve flaps. Furthermore, the possibility is described to provide air outlets between several components arranged sequentially within a cooling airflow, the cooling airflow for the single components being individually adjustable by the outlets. The cooling concept described in the mentioned document, however, requires a cooling airflow generated by a fan.
Furthermore, in document DE 20 2006 008 792 U1 a solar inverter is shown comprising an angled course of a cooling air channel between an inlet and an outlet for cooling air.
For an inverter of a PV system the converted power varies significantly depending on insolation conditions of the solar radiation. For reasons of energy efficiency it is desirable within the partial load regime of the inverter to not generate the cooling airflow actively by a fan, but to achieve a sufficient cooling in the partial load regime solely by convection. This way, the low PV power of a PV generator is not further reduced by the power consumption of the fan.